1. Field of the Invention
The present invention relates to a transducer which is used in a bonding apparatus and to a bonding apparatus which is structured to include the transducer.
2. Prior Art
In a bonding apparatus including wire bonding apparatuses, a transducer such as an ultrasonic horn and the like is used. Bonding is accomplished by applying a load and ultrasonic vibrations to the bonding section of the horn by causing the transducer to vibrate in the lengthwise direction (axial direction) of the transducer by a vibrator and at the same time by lowering a bonding tool mounted at the tip end of the transducer toward the object of process (bonding) and applying a load thereto.
A conventional supporting structure for such a transducer used in a wire bonding apparatus (not shown) is shown in FIG. 6.
In this transducer, a capillary 66 used as a bonding tool. The capillary 66 is attached to the tip end of an ultrasonic horn 51 that is used as a transducer, and a wire (not shown) passes through the capillary 66. An ultrasonic vibrator 90 is fastened to the base end of the ultrasonic horn 51. A flange 54 which has a cylindrical shape and is connected to the ultrasonic horn 51 at the front end of said flange 54 is disposed on the ultrasonic horn 51. The flange 54 is provided so that it is at a node (i.e., a point where the strain reaches the maximum) position of the ultrasonic vibration, which is applied as a compressional wave (longitudinal wave) in the axial direction, i.e., the direction of length of the horn 51. The flange 54 is connected to a cylindrical horn support 55. The horn support 55 is fastened to a transducer holder 56, and this transducer holder 56 is fastened to a supporting shaft 57. The supporting shaft 57 is supported on a bonding head (not shown) of the bonding apparatus either directly or via a lifter arm, so that the supporting shaft 57 is free to rotate.
Wire bonding apparatuses of this type are disclosed in, for example, Japanese Patent Application Laid-Open (Kokai) Nos. 5-347334, 6-196532 and 10-303240.
In the above prior art, the flange 54 is disposed at a node position of the ultrasonic vibration in the ultrasonic horn 51. Accordingly, the energy loss (so-called leakage) via this flange 54 is small; and thus, a defective crushed shape of the ball, stripping of the ball or damage to the substrate, etc., caused by the continued application of unnecessary ultrasonic energy following the completion of bonding can be prevented.
However, as the operation of the bonding apparatus is performed at higher speeds, oscillation during the raising and lowering movement of the transducer becomes a problem. In this respect, since the ultrasonic horn 51 in the above prior art is supported at only one place, it is difficult to effectively suppress the oscillation of the transducer caused by the operation of the bonding head. When such oscillation occurs, an excessive force is applied to the ball during bonding, and defects in the crushed shape of the ball occur. This problem is especially conspicuous in the diameters of press-bonded balls that have been reduced as a result of the increasingly finer pitch of recent semiconductor devices.
In order to deal with oscillation of the transducer during the raising and lowering movement of the transducer, the applicant of the present invention has proposed in Japanese Patent Application Laid-Open (Kokai) No. 2001-24025 a transducer structure as shown in FIG. 7.
In this structure, an ultrasonic horn 101 used as a transducer is attached to a transducer holder 106 via two horn supporting members 105 that are separate elements from the ultrasonic horn 101. The attachment positions of the horn supporting members 105 in the axial direction of the ultrasonic horn 101 are adjustable. In this structure, since there are two supporting points, oscillation during the raising and lowering movement of the ultrasonic horn 101 can be effectively prevented. Furthermore, a loss of the ultrasonic vibration (compressional wave) in the axial direction of the horn can also be prevented by causing the attachment positions of the horn supporting members 105 with respect to the ultrasonic horn 101 to coincide with node positions of the vibration of the ultrasonic horn 101.
Incidentally, as the regions where the horn supporting members (horn supporting members 105 in the structure of FIG. 7) are connected to the ultrasonic horn become larger (thicker) in the direction of length of the ultrasonic horn, the portions of these regions that are away from the nodes of the vibration increase. As a result, there is a corresponding increase in the energy loss. More specifically, in order to reduce the energy loss that occurs via the horn supporting members, it is desirable to form the horn supporting members as thin as possible in the axial direction of the ultrasonic horn. However, if the horn supporting members are thin, then there is a corresponding drop in the strength of the horn supporting members.
Furthermore, in the structure in which the ultrasonic horn 51 is supported at a single point as shown in FIG. 6, the cutting work for forming the cylindrical flange 54 into a cylindrical shape that is open at one end is difficult, and it is also difficult to reduce the size of the ultrasonic horn 51. Moreover, in the structure that uses two horn supporting members 105 that are independent elements from the ultrasonic horn 101 as shown in FIG. 7, the total number of parts increases, and assembly becomes bothersome.
Accordingly, the object of the present invention is to provide a transducer having a structure that provides the supporting members of the transducer with strength and that makes it possible to form such supporting members as thin as possible in the axial direction of the transducer.
The above object is accomplished by a unique structure for a transducer which is caused to vibrate by an operation of a vibrator, and the transducer of the present invention comprises: holding portions which are provided in at least two areas that include nodes (or node positions) of vibration in a transducer main body, and connecting portions that connect the holding portions to each other at areas that differ from areas where the holding portions protrude from the transducer main body; and further the transducer main body, the holding portions and the connecting portions are integrally formed from a single material member.
In the structure of the above-described transducer of the present invention, the holding portions are disposed in at least two areas that include nodes of vibration in the transducer main body. Accordingly, oscillation of the transducer is prevented without causing a vibrational energy loss in the axial direction of the transducer. Furthermore, in the transducer of the present invention, the connecting portions that connect the holding portions to each other are provided at areas that differ from areas where the holding portions protrude from the transducer main body. Accordingly, the external force applied to one of the holding portions is dispersed in each of the respective holding portions connected by the connecting portions, and deformation of the holding portions is prevented. Accordingly, the respective holding portions can be formed extremely thin in the axial direction of the transducer main body.
Furthermore, since the transducer main body, holding portions and connecting portions are formed integrally from the same member, a sufficient strength is secured at the connection areas between the holding portions and the transducer main body, and the holding portions can be made even thinner.
In the transducer of the present invention, the holding portions have a plate-form, and they are disposed in a direction of operation of the transducer main body.
Since the plate-form holding portions are disposed in the direction of operation of the transducer main body, the cross-section of the connection areas between the transducer main body and the holding portions have a shape in which the direction of the length of such areas is equal to the direction of operation of the transducer. Consequently, even in the case of bonding that accompanies large load, a large cross-section is secured at the connection areas between the transducer main body and the holding portions, and the ability to withstand shearing increases.
Furthermore, in the transducer of the present invention, of the holding portions, one holding portion is disposed at an n-th node (n is a natural number) position from the base end of the transducer main body, and another holding portion is disposed at an n+m-th node (m is an odd number) position; and the connecting portions are provided with fastening means for fastening the connecting portions of the transducer to a transducer holder.
Generally, the vibrational characteristics of a transducer, and especially the characteristic vibration frequency and the vibration period that is the reciprocal of this frequency, are not always the same in individual transducers. In other words, it is considered that a slight variation occurs depending on the working precision, etc. In this regard, the transducer of the present invention is designed so that one holding portion is disposed at the n-th node (n is a natural number) position from the base end of the transducer main body, and another holding portion is disposed at the n+m-th node (m is an odd number) position from the base end of the transducer main body. Accordingly, even in cases where the actual positions of the nodes of vibration are shifted from the designed positions as a result of variation in the vibrational characteristics, the forces acting on the respective holding portions have opposite phases, and thus such forces are cancelled each other in the connecting portions. Accordingly, with the transducer of the present invention, it is possible to avoid such a situation that the energy that leaks out of the transducer main body via the respective holding portions is transmitted as a vibration to the transducer holder that is fastened by the fastening means or to the bonding head driving mechanism that is fastened to this transducer holder.
Furthermore, in the transducer of the present invention, the fastening means are disposed at at least two different locations in a direction of length of the connecting portions of the transducer.
In this structure, since the fastening means are disposed at at least two different points in the direction of length of the connecting portions, oscillation in the direction of operation of the transducer is effectively suppressed.
Furthermore, in the transducer of the present invention, the fastening means are respectively disposed in positions that are equal to each other in terms of length of vibration transmission paths that are formed by the holding portions and the connecting portions.
In this structure, the respective fastening means are disposed in positions that are equal to each other in terms of the length of the vibration transmission paths that are formed by the holding portions and connecting portions. Accordingly, the forces that act on the respective holding portions from the transducer main body have opposite phases at the positions of the fastening means.
Furthermore, in the transducer of the present invention, the holding portions and the connecting portions are disposed on both sides of the axial center of the transducer main body so that the holding portions and the connecting portions are symmetric with respect to the axial center of the transducer.
In this structure, the holding portions and connecting portions are disposed on both sides of the axial center of the transducer main body, and these elements are positionally symmetrical with respect to the axial center. Accordingly, as to two holding portions that are disposed symmetrically on either side of a given node of vibration, the directions of the forces caused by leakage of the vibration of the vibrator are mutually opposite directions. Thus, by way of fastening both of these holding portions to a transducer holder, the leaking energies are cancelled out each other, and the transmission of vibration to the transducer holder or to the bonding head driving mechanism to which this transducer holder is fastened is prevented.
Furthermore, in the transducer of the present invention, the holding portions and the connecting portions are provided in directions that cross (at right angles) the direction of operation of the transducer.
Accordingly, by utilizing the connecting portions so as to fasten the transducer main body to a transducer holder or to the bonding head driving mechanism, it is possible to increase the dimension of the transducer main body in the direction of operation and especially to increase the clearance on the underside of the transducer main body when the direction of operation is set to be oriented downward.
Furthermore, the transducer of the present invention includes thin portions disposed between the holding portions and the connecting portions so as to absorb vibrations.
With this structure, the transmission of vibrational energy from the holding portions to the connecting portions is buffered by the elastic deformation of the thin portions even in cases where vibrational energy leaks from the transducer main body.
The transducer of the present invention is obtained by forming through-holes in a matrix material for the transducer main body and by forming the holding portions and the connecting portions around the through-holes.
Since the transducer is manufactured by forming through-holes in a matrix material that constitutes the transducer main body and then by forming the holding portions and connecting portions around through-holes, working is simple even in cases where any working method such as cutting, casting, etc. is employed.
When the above-described transducer is used in a bonding apparatus, the advantages and effect described above with reference to the transducer are obtained.